1//===- FuzzedDataProvider.h - Utility header for fuzz targets ---*- C++ -* ===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8// A single header library providing an utility class to break up an array of
9// bytes. Whenever run on the same input, provides the same output, as long as
10// its methods are called in the same order, with the same arguments.
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
14#define LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
15
16#include <algorithm>
17#include <array>
18#include <climits>
19#include <cstddef>
20#include <cstdint>
21#include <cstdlib>
22#include <cstring>
23#include <initializer_list>
24#include <limits>
25#include <string>
26#include <type_traits>
27#include <utility>
28#include <vector>
29
30// In addition to the comments below, the API is also briefly documented at
31// https://github.com/google/fuzzing/blob/master/docs/split-inputs.md#fuzzed-data-provider
32class FuzzedDataProvider {
33 public:
34 // |data| is an array of length |size| that the FuzzedDataProvider wraps to
35 // provide more granular access. |data| must outlive the FuzzedDataProvider.
36 FuzzedDataProvider(const uint8_t *data, size_t size)
37 : data_ptr_(data), remaining_bytes_(size) {}
38 ~FuzzedDataProvider() = default;
39
40 // See the implementation below (after the class definition) for more verbose
41 // comments for each of the methods.
42
43 // Methods returning std::vector of bytes. These are the most popular choice
44 // when splitting fuzzing input into pieces, as every piece is put into a
45 // separate buffer (i.e. ASan would catch any under-/overflow) and the memory
46 // will be released automatically.
47 template <typename T> std::vector<T> ConsumeBytes(size_t num_bytes);
48 template <typename T>
49 std::vector<T> ConsumeBytesWithTerminator(size_t num_bytes, T terminator = 0);
50 template <typename T> std::vector<T> ConsumeRemainingBytes();
51
52 // Methods returning strings. Use only when you need a std::string or a null
53 // terminated C-string. Otherwise, prefer the methods returning std::vector.
54 std::string ConsumeBytesAsString(size_t num_bytes);
55 std::string ConsumeRandomLengthString(size_t max_length);
56 std::string ConsumeRandomLengthString();
57 std::string ConsumeRemainingBytesAsString();
58
59 // Methods returning integer values.
60 template <typename T> T ConsumeIntegral();
61 template <typename T> T ConsumeIntegralInRange(T min, T max);
62
63 // Methods returning floating point values.
64 template <typename T> T ConsumeFloatingPoint();
65 template <typename T> T ConsumeFloatingPointInRange(T min, T max);
66
67 // 0 <= return value <= 1.
68 template <typename T> T ConsumeProbability();
69
70 bool ConsumeBool();
71
72 // Returns a value chosen from the given enum.
73 template <typename T> T ConsumeEnum();
74
75 // Returns a value from the given array.
76 template <typename T, size_t size> T PickValueInArray(const T (&array)[size]);
77 template <typename T, size_t size>
78 T PickValueInArray(const std::array<T, size> &array);
79 template <typename T> T PickValueInArray(std::initializer_list<const T> list);
80
81 // Writes data to the given destination and returns number of bytes written.
82 size_t ConsumeData(void *destination, size_t num_bytes);
83
84 // Reports the remaining bytes available for fuzzed input.
85 size_t remaining_bytes() { return remaining_bytes_; }
86
87 private:
88 FuzzedDataProvider(const FuzzedDataProvider &) = delete;
89 FuzzedDataProvider &operator=(const FuzzedDataProvider &) = delete;
90
91 void CopyAndAdvance(void *destination, size_t num_bytes);
92
93 void Advance(size_t num_bytes);
94
95 template <typename T>
96 std::vector<T> ConsumeBytes(size_t size, size_t num_bytes);
97
98 template <typename TS, typename TU> TS ConvertUnsignedToSigned(TU value);
99
100 const uint8_t *data_ptr_;
101 size_t remaining_bytes_;
102};
103
104// Returns a std::vector containing |num_bytes| of input data. If fewer than
105// |num_bytes| of data remain, returns a shorter std::vector containing all
106// of the data that's left. Can be used with any byte sized type, such as
107// char, unsigned char, uint8_t, etc.
108template <typename T>
109std::vector<T> FuzzedDataProvider::ConsumeBytes(size_t num_bytes) {
110 num_bytes = std::min(a: num_bytes, b: remaining_bytes_);
111 return ConsumeBytes<T>(num_bytes, num_bytes);
112}
113
114// Similar to |ConsumeBytes|, but also appends the terminator value at the end
115// of the resulting vector. Useful, when a mutable null-terminated C-string is
116// needed, for example. But that is a rare case. Better avoid it, if possible,
117// and prefer using |ConsumeBytes| or |ConsumeBytesAsString| methods.
118template <typename T>
119std::vector<T> FuzzedDataProvider::ConsumeBytesWithTerminator(size_t num_bytes,
120 T terminator) {
121 num_bytes = std::min(a: num_bytes, b: remaining_bytes_);
122 std::vector<T> result = ConsumeBytes<T>(num_bytes + 1, num_bytes);
123 result.back() = terminator;
124 return result;
125}
126
127// Returns a std::vector containing all remaining bytes of the input data.
128template <typename T>
129std::vector<T> FuzzedDataProvider::ConsumeRemainingBytes() {
130 return ConsumeBytes<T>(remaining_bytes_);
131}
132
133// Returns a std::string containing |num_bytes| of input data. Using this and
134// |.c_str()| on the resulting string is the best way to get an immutable
135// null-terminated C string. If fewer than |num_bytes| of data remain, returns
136// a shorter std::string containing all of the data that's left.
137inline std::string FuzzedDataProvider::ConsumeBytesAsString(size_t num_bytes) {
138 static_assert(sizeof(std::string::value_type) == sizeof(uint8_t),
139 "ConsumeBytesAsString cannot convert the data to a string.");
140
141 num_bytes = std::min(a: num_bytes, b: remaining_bytes_);
142 std::string result(
143 reinterpret_cast<const std::string::value_type *>(data_ptr_), num_bytes);
144 Advance(num_bytes);
145 return result;
146}
147
148// Returns a std::string of length from 0 to |max_length|. When it runs out of
149// input data, returns what remains of the input. Designed to be more stable
150// with respect to a fuzzer inserting characters than just picking a random
151// length and then consuming that many bytes with |ConsumeBytes|.
152inline std::string
153FuzzedDataProvider::ConsumeRandomLengthString(size_t max_length) {
154 // Reads bytes from the start of |data_ptr_|. Maps "\\" to "\", and maps "\"
155 // followed by anything else to the end of the string. As a result of this
156 // logic, a fuzzer can insert characters into the string, and the string
157 // will be lengthened to include those new characters, resulting in a more
158 // stable fuzzer than picking the length of a string independently from
159 // picking its contents.
160 std::string result;
161
162 // Reserve the anticipated capacity to prevent several reallocations.
163 result.reserve(res: std::min(a: max_length, b: remaining_bytes_));
164 for (size_t i = 0; i < max_length && remaining_bytes_ != 0; ++i) {
165 char next = ConvertUnsignedToSigned<char>(value: data_ptr_[0]);
166 Advance(num_bytes: 1);
167 if (next == '\\' && remaining_bytes_ != 0) {
168 next = ConvertUnsignedToSigned<char>(value: data_ptr_[0]);
169 Advance(num_bytes: 1);
170 if (next != '\\')
171 break;
172 }
173 result += next;
174 }
175
176 result.shrink_to_fit();
177 return result;
178}
179
180// Returns a std::string of length from 0 to |remaining_bytes_|.
181inline std::string FuzzedDataProvider::ConsumeRandomLengthString() {
182 return ConsumeRandomLengthString(max_length: remaining_bytes_);
183}
184
185// Returns a std::string containing all remaining bytes of the input data.
186// Prefer using |ConsumeRemainingBytes| unless you actually need a std::string
187// object.
188inline std::string FuzzedDataProvider::ConsumeRemainingBytesAsString() {
189 return ConsumeBytesAsString(num_bytes: remaining_bytes_);
190}
191
192// Returns a number in the range [Type's min, Type's max]. The value might
193// not be uniformly distributed in the given range. If there's no input data
194// left, always returns |min|.
195template <typename T> T FuzzedDataProvider::ConsumeIntegral() {
196 return ConsumeIntegralInRange(std::numeric_limits<T>::min(),
197 std::numeric_limits<T>::max());
198}
199
200// Returns a number in the range [min, max] by consuming bytes from the
201// input data. The value might not be uniformly distributed in the given
202// range. If there's no input data left, always returns |min|. |min| must
203// be less than or equal to |max|.
204template <typename T>
205T FuzzedDataProvider::ConsumeIntegralInRange(T min, T max) {
206 static_assert(std::is_integral_v<T>, "An integral type is required.");
207 static_assert(sizeof(T) <= sizeof(uint64_t), "Unsupported integral type.");
208
209 if (min > max)
210 abort();
211
212 // Use the biggest type possible to hold the range and the result.
213 uint64_t range = static_cast<uint64_t>(max) - static_cast<uint64_t>(min);
214 uint64_t result = 0;
215 size_t offset = 0;
216
217 while (offset < sizeof(T) * CHAR_BIT && (range >> offset) > 0 &&
218 remaining_bytes_ != 0) {
219 // Pull bytes off the end of the seed data. Experimentally, this seems to
220 // allow the fuzzer to more easily explore the input space. This makes
221 // sense, since it works by modifying inputs that caused new code to run,
222 // and this data is often used to encode length of data read by
223 // |ConsumeBytes|. Separating out read lengths makes it easier modify the
224 // contents of the data that is actually read.
225 --remaining_bytes_;
226 result = (result << CHAR_BIT) | data_ptr_[remaining_bytes_];
227 offset += CHAR_BIT;
228 }
229
230 // Avoid division by 0, in case |range + 1| results in overflow.
231 if (range != std::numeric_limits<decltype(range)>::max())
232 result = result % (range + 1);
233
234 return static_cast<T>(static_cast<uint64_t>(min) + result);
235}
236
237// Returns a floating point value in the range [Type's lowest, Type's max] by
238// consuming bytes from the input data. If there's no input data left, always
239// returns approximately 0.
240template <typename T> T FuzzedDataProvider::ConsumeFloatingPoint() {
241 return ConsumeFloatingPointInRange<T>(std::numeric_limits<T>::lowest(),
242 std::numeric_limits<T>::max());
243}
244
245// Returns a floating point value in the given range by consuming bytes from
246// the input data. If there's no input data left, returns |min|. Note that
247// |min| must be less than or equal to |max|.
248template <typename T>
249T FuzzedDataProvider::ConsumeFloatingPointInRange(T min, T max) {
250 if (min > max)
251 abort();
252
253 T range = .0;
254 T result = min;
255 constexpr T zero(.0);
256 if (max > zero && min < zero && max > min + std::numeric_limits<T>::max()) {
257 // The diff |max - min| would overflow the given floating point type. Use
258 // the half of the diff as the range and consume a bool to decide whether
259 // the result is in the first of the second part of the diff.
260 range = (max / 2.0) - (min / 2.0);
261 if (ConsumeBool()) {
262 result += range;
263 }
264 } else {
265 range = max - min;
266 }
267
268 return result + range * ConsumeProbability<T>();
269}
270
271// Returns a floating point number in the range [0.0, 1.0]. If there's no
272// input data left, always returns 0.
273template <typename T> T FuzzedDataProvider::ConsumeProbability() {
274 static_assert(std::is_floating_point_v<T>,
275 "A floating point type is required.");
276
277 // Use different integral types for different floating point types in order
278 // to provide better density of the resulting values.
279 using IntegralType =
280 typename std::conditional_t<(sizeof(T) <= sizeof(uint32_t)), uint32_t,
281 uint64_t>;
282
283 T result = static_cast<T>(ConsumeIntegral<IntegralType>());
284 result /= static_cast<T>(std::numeric_limits<IntegralType>::max());
285 return result;
286}
287
288// Reads one byte and returns a bool, or false when no data remains.
289inline bool FuzzedDataProvider::ConsumeBool() {
290 return 1 & ConsumeIntegral<uint8_t>();
291}
292
293// Returns an enum value. The enum must start at 0 and be contiguous. It must
294// also contain |kMaxValue| aliased to its largest (inclusive) value. Such as:
295// enum class Foo { SomeValue, OtherValue, kMaxValue = OtherValue };
296template <typename T> T FuzzedDataProvider::ConsumeEnum() {
297 static_assert(std::is_enum_v<T>, "|T| must be an enum type.");
298 return static_cast<T>(
299 ConsumeIntegralInRange<uint32_t>(min: 0, max: static_cast<uint32_t>(T::kMaxValue)));
300}
301
302// Returns a copy of the value selected from the given fixed-size |array|.
303template <typename T, size_t size>
304T FuzzedDataProvider::PickValueInArray(const T (&array)[size]) {
305 static_assert(size > 0, "The array must be non empty.");
306 return array[ConsumeIntegralInRange<size_t>(min: 0, max: size - 1)];
307}
308
309template <typename T, size_t size>
310T FuzzedDataProvider::PickValueInArray(const std::array<T, size> &array) {
311 static_assert(size > 0, "The array must be non empty.");
312 return array[ConsumeIntegralInRange<size_t>(min: 0, max: size - 1)];
313}
314
315template <typename T>
316T FuzzedDataProvider::PickValueInArray(std::initializer_list<const T> list) {
317 if (!list.size())
318 abort();
319
320 return *(list.begin() + ConsumeIntegralInRange<size_t>(0, list.size() - 1));
321}
322
323// Writes |num_bytes| of input data to the given destination pointer. If there
324// is not enough data left, writes all remaining bytes. Return value is the
325// number of bytes written.
326// In general, it's better to avoid using this function, but it may be useful
327// in cases when it's necessary to fill a certain buffer or object with
328// fuzzing data.
329inline size_t FuzzedDataProvider::ConsumeData(void *destination,
330 size_t num_bytes) {
331 num_bytes = std::min(a: num_bytes, b: remaining_bytes_);
332 CopyAndAdvance(destination, num_bytes);
333 return num_bytes;
334}
335
336// Private methods.
337inline void FuzzedDataProvider::CopyAndAdvance(void *destination,
338 size_t num_bytes) {
339 std::memcpy(dest: destination, src: data_ptr_, n: num_bytes);
340 Advance(num_bytes);
341}
342
343inline void FuzzedDataProvider::Advance(size_t num_bytes) {
344 if (num_bytes > remaining_bytes_)
345 abort();
346
347 data_ptr_ += num_bytes;
348 remaining_bytes_ -= num_bytes;
349}
350
351template <typename T>
352std::vector<T> FuzzedDataProvider::ConsumeBytes(size_t size, size_t num_bytes) {
353 static_assert(sizeof(T) == sizeof(uint8_t), "Incompatible data type.");
354
355 // The point of using the size-based constructor below is to increase the
356 // odds of having a vector object with capacity being equal to the length.
357 // That part is always implementation specific, but at least both libc++ and
358 // libstdc++ allocate the requested number of bytes in that constructor,
359 // which seems to be a natural choice for other implementations as well.
360 // To increase the odds even more, we also call |shrink_to_fit| below.
361 std::vector<T> result(size);
362 if (size == 0) {
363 if (num_bytes != 0)
364 abort();
365 return result;
366 }
367
368 CopyAndAdvance(destination: result.data(), num_bytes);
369
370 // Even though |shrink_to_fit| is also implementation specific, we expect it
371 // to provide an additional assurance in case vector's constructor allocated
372 // a buffer which is larger than the actual amount of data we put inside it.
373 result.shrink_to_fit();
374 return result;
375}
376
377template <typename TS, typename TU>
378TS FuzzedDataProvider::ConvertUnsignedToSigned(TU value) {
379 static_assert(sizeof(TS) == sizeof(TU), "Incompatible data types.");
380 static_assert(!std::numeric_limits<TU>::is_signed,
381 "Source type must be unsigned.");
382
383 // TODO(Dor1s): change to `if constexpr` once C++17 becomes mainstream.
384 if (std::numeric_limits<TS>::is_modulo)
385 return static_cast<TS>(value);
386
387 // Avoid using implementation-defined unsigned to signed conversions.
388 // To learn more, see https://stackoverflow.com/questions/13150449.
389 if (value <= std::numeric_limits<TS>::max()) {
390 return static_cast<TS>(value);
391 } else {
392 constexpr auto TS_min = std::numeric_limits<TS>::min();
393 return TS_min + static_cast<TS>(value - TS_min);
394 }
395}
396
397#endif // LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
398

source code of compiler-rt/include/fuzzer/FuzzedDataProvider.h